1. Technical Field of the Invention
The present invention relates in general to the configuration of radio base stations and, in particular, to a method and system for autonomously determining the configuration of a radio base station in a cellular telecommunications system.
2. Description of Related Art
A base transceiver station in a cellular telecommunications system comprises the necessary hardware for supporting communications in one cell of a cellular system. Generally, a base transceiver station includes one or more antennas, one or more transceivers, and a number of combining/distribution units that contain various signal processing and/or routing devices for interconnecting the antennas and the transceivers. These signal processing and routing devices in the combining/distribution units can include, for example, filters, duplexers, amplifiers, signal combiners, and signal splitters. A combining/distribution unit can also be integrated in an antenna (e.g., a xe2x80x9ctower mounted amplifierxe2x80x9d). Radio signals received by a single antenna are often split by the combining/distribution units and routed to several different transceivers. In the transmission direction, on the other hand, radio telecommunications signals from multiple transceivers are often combined and routed to a single antenna. The routing and processing operations of the base transceiver station can widely vary, however, and are typically dependent on the desired characteristics for the particular cell.
One or more such base transceiver stations can be incorporated into a single radio base station of the cellular telecommunications system. The number of base transceiver stations is normally dictated by the number of cells served by the base station. An xe2x80x9comnixe2x80x9d radio base station site, for instance, provides 360 degree radio coverage in a single cell. Thus, only one base transceiver station is needed. A two sector site, on the other hand, provides radio coverage for two different areas (i.e. two cells) and two base transceiver stations are needed. Similarly, a three sector site supports radio communications in three cells and uses three base transceiver stations.
A radio base station can be configured into hundreds, or even thousands, of distinct configurations. A particular configuration depends on and is defined by the number of base transceiver stations in the radio base station and on the number, arrangement, and interconnection of combining/distribution units in each base transceiver station. Some typical measures for classifying different radio base station configurations and for differentiating between various configurations are:
(1) the number of antenna systems used by the base station (an antenna system is a set of antennas that is used for receiving and transmitting signals in a specific cell);
(2) the number of transceivers per cell;
(3) the number of implemented receive branches (e.g., a base transceiver station of the base station can be configured so that signals of a particular frequency are received by an antenna and transmitted over a single signal path to a single transceiver, or so that signals of that frequency are routed over multiple signal paths to more than one transceiver); and
(4) the amount of signal combining (i.e., the combining of signals from multiple transceivers for transmission from a single antenna or antenna system) that is performed by each combining/distribution unit for the transmission of radio signals from the base station.
The selection of a configuration for use in a particular radio base station typically depends upon the desired operational characteristics of the base station. This is because the different measures listed above directly correspond to certain functional attributes of the base station. For example, the number of antenna systems used depends on how many cells are served by the radio base station. Each cell to be served requires its own antenna system. In addition, the number of transceivers in a given cell affects the offered traffic capacity for that cell. The offered traffic capacity is essentially the maximum traffic flow in a cellular system or part of a cellular system. The number of transceivers used in a base station, therefore, is typically determined according to a desired amount of offered traffic capacity and a tolerable probability of call failures (i.e., due to the cell reaching its call capacity). The desired reception diversity is a third factor that affects the number of receive branches in the configuration. To improve reception at the base station, especially in cases where the signals from a mobile station are somewhat impeded, the number of implemented receive branches should be increased. Finally, combining of signals in the combining/distribution unit causes losses in radio frequency signals to be transmitted. Accordingly, to obtain maximum transmission output power, and thus to obtain the maximum achievable geographic coverage, any combining of signals to be transmitted should be minimized. Thus, the selection of a configuration in a base station is typically influenced by factors such as the number of cells to be served, the expected amount of cellular traffic, the amount of interference in the cell, the size of the cell, and the desired output power and receiver sensitivity for the base station.
A radio base station is capable of implementing any one of a large number of distinct radio configurations. To do so, however, an operator of the radio base station must install a specific radio configuration file. Each radio configuration file comprises a set of data specifying how the transceivers are connected to the antenna systems in both the transmit and receive directions, and what hardware components (i.e., what devices within the combining/distribution units) are used to provide the RF signal paths. Each radio configuration file thereby defines a particular radio transmission and reception functionality. Installation of a radio configuration file is necessary because knowledge about the currently implemented radio configuration, as provided by the installed file, can be required to support several routine functions of the base station, such as calibration or supervision of the various devices in the base station. Typically, a vendor of a base station system develops radio configuration files for a significant number of distinct configurations. Certain ones of these files, selected according to a customer""s particular needs, are then provided to the customer for installation into a radio base station.
The use of base station systems that require these individual, fixed radio configuration files has several major disadvantages. First, if the radio configuration of a base station is significantly changed, a new radio configuration file must be loaded into the base station. Such an upgrade requires the selection of an appropriate configuration file. In addition, the installation of the new configuration file requires a certain degree of technical knowledge by the person performing the installation. Moreover, if a different radio configuration file has to be loaded, the complete base station usually has to be taken out of operation, interrupting cellular traffic in that cell.
Changes in the configuration are common and often occur when the desired functional characteristics of the base station change. Such a change can occur, for instance, in the case of a cell split, wherein an omni-directional cell (i.e., an xe2x80x9comnixe2x80x9d site) is split into two or more sectorized cells (e.g., a two sector site, as described above), which would necessitate, at a minimum, a change in the number of antenna systems that are used.
A configuration change can also occur when a base station is upgraded to have a higher offered traffic capacity. When a base station system is initially installed, the base station often has a limited cellular traffic capacity because, for instance, initial use in the cells served by the base station is relatively low. Over time, however, a higher traffic capacity might be required as use of the system increases. To increase capacity, the base station must be upgraded to include more hardware equipment. Typically, several configuration options exist for such an upgrade, and when the system is initially installed, it is difficult to predict which configuration will be implemented in the future. Thus, when the system is upgraded, a new configuration file must be installed.
In addition to the disadvantages that result from changes in the configuration, other problems with the current base station set-up exist as well. To support the many different possible configurations, a huge number of radio configuration files need to be developed, implemented, maintained, and handled. Furthermore, in some cases, configuration files may not be available for a particular desired configuration.
There is a need, therefore, for a system and method for permitting a radio base station to autonomously determine and adapt to new configurations. This type of system and method would make a base station system more flexible and easier to handle. The configuration of the base station could be changed, if necessary, on a more frequent basis, and such changes would not require that new configuration files be loaded into the base station. Furthermore, a system and method is needed that would eliminate the need to develop, implement, and maintain large numbers of configuration files and that would significantly reduce the amount of time that base stations are removed from operation, or operate under reduced capacity, for the installation of new configuration files.
The present invention comprises an autonomous exploration and recognition method and system for identifying an implemented radio configuration for a radio base station in a telecommunications system. According to the invention, radio configuration information signals, comprising a controlled DC voltage variation or digital signal, are transmitted from the antenna interfaces of the base station to the transceivers in the base station along each different RF signal path. Generally, the radio configuration information signals are transmitted from an inbound port (i.e., a combining/distribution unit port on the transceiver side of the combining/distribution unit) to an outbound port (i.e., a combining/distribution unit port on the antenna side of the combining/distribution unit) of interconnected combining/distribution units or, for the last segment of the signal path, from an inbound port of a combining/distribution unit to a port of a transceiver.
Once the radio configuration information signals have propagated through the base station along each of the various signal paths, the transceiver is able to identify the various interconnections between antennas, combining/distribution units, and transceivers along the particular signal path. Using a digital interface between the transceiver and the combining/distribution unit, the transceiver is also able to access information about the internal structure of the combining/distribution units. Thus, the transceivers can collectively determine the radio configuration for the entire base station, and supervision and control functions can be performed accordingly.
The invention can be implemented using a radio configuration information data transfer circuit (for transmitting radio configuration information signals between interconnected combining/distribution units or between a combining/distribution unit and an interconnected transceiver). The data transfer circuit includes a signal generator for encoding the outgoing radio configuration information data (e.g., using digital signals or controlled variations in a DC voltage level). The signal generator is contained in a first combining/distribution unit (or, in general, in the first unit which is located at an end of the signal path to be explored) and is coupled to one end of a cable or a pair of track conductors (or some other type of interconnection) that carries RF signals along a particular signal path and that interconnects the first combining/distribution unit with a second combining/distribution unit or, alternatively, with a different port of the first combining/distribution unit. The second combining/distribution unit includes a signal detector that is coupled to the other end of the cable or other interface and that detects signals from the signal generator. In the same way, the second combining/distribution unit could be connected to a third one and so on. In general, an arbitrary number of combining/distribution units and ports can be handled. Generally, each unit contains signal detectors at outbound ports and signal generators at inbound ports.
Each combining/distribution unit also includes a radio configuration information control circuit for controlling the generation and routing of radio configuration information signals. The control circuit receives radio configuration information signals from the signal detectors and routes the radio configuration information signals to the signal generators of the combining/distribution unit. Preferably, the radio configuration information control circuit is implemented using an application specific integrated circuit and contains circuitry necessary for decoding, storing, routing, and re-coding of radio configuration information signals received from one of the combining/distribution unit""s outbound ports. The radio configuration information control circuit transmits the radio configuration information signals to corresponding inbound ports according to the internal RF connections for the combining/distribution unit. In addition, upon initiation of the radio configuration information message generation sequence, the radio configuration information control circuit also generates radio configuration information data for the specific combining/distribution unit itself and transmits the data to the appropriate inbound ports. Thus, each inbound port receives the radio configuration information data for the combining/distribution unit with which it is associated.